Geometry and spatial organization are critical components in many biological systems. The importance of geometry and spatial organization can be seen within the immune system in a variety of ways including during the interaction of a T cell with an antigen presenting cell (APC), which is a critical determinant of T cell fate and effector function. With activation, APC, such as dendritic cells (DC), have major changes in their cell morphology, which results in a significant increase in their overall cell surface area. Such changes in cell morphology facilitate interaction with naïve T cells and ultimately affect T cell fate and outcome. T cell activation is further modulated by the formation of a large surface area of close membrane apposition between the DC and T cell membrane termed the “immune synapse.” Grakoui, A., et al., The immunological synapse: a molecular machine controlling T cell activation. Science 285, 221-227 (1999). Monks, C. R., et al., Three-dimensional segregation of supramolecular activation clusters in T cells. Nature 395, 82-86 (1998). Lee, K. H., et al., T cell receptor signaling precedes immunological synapse formation. Science 295, 1539-1542 (2002). Thus, taking into account the geometry and spatial organization is important in studying biological responses.
Reductionist systems also have facilitated the study of effective immune responses. One such system has been the development of acellular artificial antigen presenting cells (aAPCs). These systems have been made by coupling proteins required for T cell activation to particles. Minimally, T cell activation requires two sets of receptor-receptor interactions between cells. The first interaction, Signal 1, is the binding of major histocompatibility complexes (MHC) or a surrogate, such as anti-CD3, to the T cell receptor (TCR). The second interaction, Signal 2, is the binding of costimulatory receptors on the APC, such as B7.1, to ligands on the T cell, such as CD28. Accordingly, aAPC have been generated by coupling proteins that deliver Signal 1 and Signal 2 to the surface of microbeads (FIG. 2a) made from a range of materials, including magnetic microparticles, Oelke, M., et al., Ex vivo induction and expansion of antigen-specific cytotoxic T cells by HLA-Ig-coated artificial antigen-presenting cells. Nat Med 9, 619-625. PMID: 12074385 (2003). Ugel, S., et al., In vivo administration of artificial antigen-presenting cells activates low-avidity T cells for treatment of cancer. Cancer Res 69, 9376-9384 (2009), polystyrene particles, Mescher, M. F. Surface contact requirements for activation of cytotoxic T lymphocytes. J Immunol 149, 2402-2405 (1992), and PLGA microparticles. Han, H., et al., A novel system of artificial antigen-presenting cells efficiently stimulates Flu peptide-specific cytotoxic T cells in vitro. Biochem Biophys Res Commun 411, 530-535 (2011). Steenblock, E. R., et al., An artificial antigen-presenting cell with paracrine delivery of IL-2 impacts the magnitude and direction of the T cell response. J Biol Chem 286, 34883-34892 (2011). Steenblock, E. R. and Fahmy, T. M. A comprehensive platform for ex vivo T cell expansion based on biodegradable polymeric artificial antigen-presenting cells. Mol Ther 16, 765-772. PMID: 18334990 (2008).
Such systems have been broadly applied to tumor immunotherapy, vaccination, and immunosuppression, and are amenable to in vivo or ex vivo T cell stimulation and offer possible novel translational approaches to immunotherapy. Ugel, S., et al., In vivo administration of artificial antigen-presenting cells activates low-avidity T cells for treatment of cancer. Cancer Res 69, 9376-9384 (2009). Ndhlovu, Z. M., et al., Dynamic regulation of functionally distinct virus-specific T cells. Proc Natl Acad Sci USA 107, 3669-3674 (2010). Ito, F., et al., Antitumor reactivity of anti-CD3/anti-CD28 bead-activated lymphoid cells: implications for cell therapy in a murine model. J Immunother 26, 222-233 (2003). Lum, L. G., et al., Immune modulation in cancer patients after adoptive transfer of anti-CD3/anti-CD28-costimulated T cells-phase I clinical trial. J Immunother 24, 408-419 (2001). Taylor, P. A., et al., The infusion of ex vivo activated and expanded CD4(+)CD25(+) immune regulatory cells inhibits graft-versus-host disease lethality. Blood 99, 3493-3499 (2002). Balmert, S. C. and Little, S. R., Biomimetic delivery with micro- and nanoparticles. Adv Mater 24, 3757-3778 (2012).
While useful, the Signal 1 and Signal 2 paradigms alone do not capture aspects of spatial organization or the geometry of interactions. Previous work developing artificial systems for stimulation of effective in vitro and in vivo T cell responses has not attempted to re-capitulate these aspects of APC behavior. As a result, all particle systems tested thus far have used spherical particles for their aAPC platforms, which unlike DC, minimize surface area for a given volume (FIG. 2b).
Particle shape has only recently become a design parameter of interest in the field of material design for drug delivery. Shape can play a role in tuning the rate and mechanism of cellular uptake, Wang, J., et al., More effective nanomedicines through particle design. Small 7, 1919-1931 (2011), can dramatically reduce internalization by phagocytic cells, such as macrophages, Champion, J. A. and Mitragotri, S., Role of target geometry in phagocytosis. Proc Natl Acad Sci USA 103, 4930-4934 (2006). Sharma, G., et al., Polymer particle shape independently influences binding and internalization by macrophages. J Control Release 147, 408-412 (2010), can change the biodistribution of the drug delivery vehicle, Champion, J. A., et al., Particle shape: a new design parameter for micro- and nanoscale drug delivery carriers. J Control Release 121, 3-9 (2007). Devarajan, P. V., et al., Particle shape: a new design parameter for passive targeting in splenotropic drug delivery. J Pharm Sci 99, 2576-2581 (2010), and can affect the ability of a particle to bind a cell, in part, by increasing the surface area for interaction. Champion, J. A., et al., Particle shape: a new design parameter for micro- and nanoscale drug delivery carriers. J Control Release 121, 3-9 (2007). Harris, B. J. and Dalhaimer, P., Particle shape effects in vitro and in vivo. Front Biosci (Schol Ed) 4, 1344-1353 (2012). Yoo, J. W. and Mitragotri, S., Polymer particles that switch shape in response to a stimulus. Proc Natl Acad Sci USA 107, 11205-11210 (2010)